1. Field of the Invention
This invention relates to fasteners for sheet materials and in particular to novel staple-like fasteners which are useful in fastening weak or gossamer sheet materials. The novel fasteners of this invention are easily removed from the sheet materials when it is desired to unfasten them. They also have a reduced tendency to "tear through" the sheet materials being fastened.
2. Description of the Prior Art
U.S. Pat. No. 3,357,296, which issued on Dec. 12, 1967 to K. W. Lefever, discloses a staple fastener in which separate prongs are detachably mounted by ball-shaped end portions in a molded plastic cross-member. A mating plastic receiving element has coaxial apertures in each end into which the exposed pointed ends of the prongs are bent by a specially designed anvil in a stapling machine. In order to disassemble the stapler after it has been applied, it is first necessary to pull the cross-member and the receiving element in opposite directions with sufficient force to detach the ball-shaped end portions of the prongs from the cross-member. Thereafter the ball-shaped end portions must be torn through the sheet material which has been stapled. Because of this detachable construction, the device of the Lefever patent is incompatible with the use of standard wire staples.
U.S. Pat. No. 2,526,902, issued Oct. 24, 1950 to N. C. Rublee, and U.S. Pat. No. 3,076,373, issued Feb. 5, 1963 to C. G. Matthews, while showing single-element staples in which at least a portion of the staple is enclosed in resin material for electrical insulation or improved driveability and holding power, do not disclose a receiving element for protecting sheet material to be stapled.
U.S. Pat. No. 644,976 issued on Mar. 6, 1900 to J. H. Gibson, discloses a wire staple for attaching a carpet to a floor. The staple simply includes a perforated disk-like head for facilitating removal of the staple. The floor serves as the receiving element.
U.S. Pat. Nos. 1,282,845 issued Oct. 29, 1918 to C. A. Johnson, No. 3,368,445 issued Feb. 13, 1968 to J. J. Trzesniewski, and No. 3,610,087 issued Oct. 5, 1971 to A. Dritz, show single-element staple devices in which the prongs are deformed in various configurations during the fastening process.